The present invention relates to a tactile switch used in a portable telephone, portable radio receiver, camera and others.
FIG. 6 is a plan view showing a conventional tactile switch, FIG. 7 is a sectional view taken along a line VIIxe2x80x94VII of FIG. 6, FIG. 8 is a plan view showing another conventional tactile switch and FIG. 9 is a sectional view taken along a line IXxe2x80x94IX of FIG. 8.
The tactile switch has a side of 4 mm and a thickness of 0.5 mm. The switch has a substrate 1, a peripheral fixed contact 5 printed on the substrate 1 and having a circular hole 5a at a central portion thereof, a central fixed contact 6, printed on the substrate 1 in the circular hole 5a, a spherical spring contact 4 mounted on the peripheral fixed contact 5 and a flexible cover 21 made of plastic and adhered to the peripheral fixed contact 5 so as to press the spring contact 4 against the peripheral fixed contact.
Each of four corners of the substrate has a semicircular recess. Four terminal electrodes 9a to 9d are secured to the semicircular recesses and to the underside of the substrate 1 in order to connect the tactile switch with an instrument to be mounted therein.
The peripheral fixed contact 5 is connected to the terminal electrode 9a. 
The central fixed contact 6 is connected to the terminal electrode 9c by a lead provided in a through-hole 7 and a conductive pattern 8.
The spring contact 4 is depressed through the cover 21 by a push button provided in the instrument, so that a central portion of the spring contact 4 is downwardly bent. The spring contact contacts with the central fixed contact 6, so that the peripheral fixed contact 5 is connected to the central fixed contact 6.
The switch shown in FIGS. 8 and 9 comprises a plurality of fixed contacts 5, 6 shown in FIGS. 6 and 7, provided on a substrate 22, a plurality of spring plates 4 and a cover 23 adhered to the substrate 22.
In the conventional switch, the cover 21 (23) contacts with the spring contact 4 at the entire surface of the spring contact 4.
Therefore, the contact area of the spring plate 4 with the central fixed contact is comparatively large. As a result, the contact pressure of the spring plate on the central fixed contact is low, which causes the reliability of the switch to decrease.
An object of the present invention is to provide a tactile switch in which the spring contact contacts with the central fixed contact at a high pressure, thereby increasing the reliability of the switch.
According to the present invention, there is provided a tactile switch comprising a substrate, a peripheral fixed contact having a circular hole and secured to the substrate, a central fixed contact having a hole at a central portion thereof and secured to the substrate within the circular hole of the peripheral fixed contact, a spherical spring contact mounted on the peripheral fixed contact so as to contact with an edge of the hole of the central fixed contact.
The hole of the central fixed contact has inward projection.
The tactile switch further comprises an annular spacer made of insulation material and secured to the substrate, and a flexible cover secured to the spacer, the spring contact being provided within the spacer.
The tactile switch further comprises marks provided on an upper surface and on underside of the switch for detecting the upper surface.